Intermodulation is the amplitude modulation of signals containing two or more different frequencies in a system with non-linearities that results in signal noise. The intermodulation between each frequency component can form additional signals at frequencies that are harmonic frequencies and sum and difference frequencies of the original frequencies and multiples thereof. The non-linearities can be cause by junctions in the physical equipment (cables, antennas), as well as by sources in the surrounding environment. This type intermodulation, caused by non-active components, is called external (in the sense the passive intermodulation sources are external to the cabling/antenna system) passive intermodulation and can be difficult and costly to diagnose as site visits by skilled technicians are traditionally used to detect and identify the non-linearity source locations.